Not too many studies these days conclude that a little sex is good, and even more sex is better.

But in one of the first major attempts to gauge the cancer risk of male sexual activity, researchers at the prestigious National Cancer Institute discovered to their great surprise that a lot of orgasms do a guy no harm -- and may even do him some good.

It matters not if they happen during sexual intercourse with a man or a woman, or if they occur spontaneously during sleep. Even masturbation, scientifically speaking, is good for you.

"As epidemiology studies go, this is about as good as it gets," said John Witte, a genetic epidemiologist at UCSF, who was not one of the study's authors but was familiar with the results. "In this day and age, when most of the health warnings are negative -- 'don't do this, don't do that' -- this is kind of a fun one. So ejaculation is something people don't have to feel bad about."

The study, which appears in the latest Journal of the American Medical Association, is by far the most ambitious attempt yet to clear away some of the confusion surrounding male sexual function and one of mankind's deadliest cancers.

This year, an estimated 230,000 men in the United States will be diagnosed with prostate cancer, and nearly 30,000 will die, making it second only to lung cancer on the list of the leading causes of male cancer deaths.

The research was done as part of the well-regarded Health Professionals Follow-up Study, a comprehensive look at the health and habits of nearly 52, 000 predominantly white middle-aged men, launched in 1986. Experts said they had no reason to suspect the results would have been substantially different if a broader population mix were included.

The prostate study includes results for 29,342 men. The health professionals filled out detailed survey forms every two years from 1992 to 2000, estimating how many ejaculations they had had per month on average during their 20s, their 40s and the past year. Sexual climaxes during intercourse and masturbation, as well as nocturnal emissions, all counted the same.

Nearly all the previous studies suggested a link between sexual activity and elevated risk of prostate cancer, possibly because of high testosterone levels or exposure to infectious agents among men engaging in frequent sex. A small study in Australia last year suggested the opposite might be true, but those results were largely dismissed.

The new study is the first careful attempt to track a large group of men for a number of years, using statistical tools to take into account differences in diet, exercise and other disease factors that might influence prostate cancer rates. All the men were cancer-free when the study began.

The questionnaires were used to divide the men into categories of sexual activity, ranging from those estimating an average four to seven orgasms a month to those reporting at least 21 per month. Only a handful of men admitted to having fewer than one orgasm a week -- not enough to make up their own category. So those few unfortunates were lumped in with the four-to-seven orgasms a month group.

Results were striking: Men having the most orgasms reduced their prostate cancer risk by a full third compared with those men reporting the fewest orgasms. The same pattern held true for those who landed in between the extremes, including an 11 percent reduced cancer risk for those estimating eight to 12 monthly ejaculations and a 14 percent decrease for those in the 13- to-20 ejaculation group.

In their formal account of their findings, the authors seemed to play down the apparent protective effects of male orgasm, in part because there is no agreement as to what might account for the protection.

"The really good news," said Dr. Michael Leitzmann, an investigator at the National Cancer Institute in Bethesda, Md., and one of the study's lead authors, is "that a high frequency of ejaculations does not increase your risk" of contracting a potentially fatal cancer as you age.

One possible explanation, said Leitzmann and other scientists, may be that the prostate accumulates carcinogens, which are perhaps cleared out during the male sex act. The walnut-size prostate gland produces fluids that are contained in semen.

Australian epidemiologist Graham Giles at the nonprofit Cancer Council in Melbourne said one of the big remaining questions was the effect of frequent orgasms during one's teenage years. Like early childbirth in women, a lot of orgasms early in a man's life span may be "like running an engine," he said, prompting youthful cells in the critical region to "fully develop into a whole lot of nice prostate cells."

But the epidemiologists said they had no intention of launching a new pro- masturbation public-health campaign aimed at teenage boys. No need for that, they said.

Prostate cancer risk
Prostate cancer is the second most common cancer in men, after skin cancer.
It occurs in about 1 in every 6 men and with greater prevalence in blacks than
whites.
Prostate cancer prevalence
Risk of being Risk of
diagnosed dying
All races 17.28% 3.05%
Blacks 20.40% 4.72%
Whites 16.9% 2.86%
Source: National Cancer Institute
Associated Press Graphic